1. Field of the Invention
The invention relates generally to the field of electrical wiring devices, and more particularly to switches such as are used in controlling room lighting, in residential and commercial buildings. In a more particular sense, the invention relates to those switches which are of the solid state, touch-controlled type, that is to say, switches in which a touch of a stationary handle plate with one's finger is adapted to close the controlled circuit, and wherein the plate is again touched, to open the circuit.
2. Description of the Prior Art
It is well known to provide touch control switching circuits, wherein an exposed plate is adapted to be touched by one's finger, to cause a circuit to be closed to a source of electrical power, for any of various uses. It is, for example, very common to provide touch plates wherein contact with the plate by one's finger produces an electronic response in which the user becomes part of an electrical circuit adapted through suitable electrical circuitry to close or open a switching circuit to a source of electrical power.
Switching circuits of this type have comparatively recently come into use as a means for controlling room lighting, in place of the conventional toggle type or push type wall switches that have been in vogue for many years. It is, indeed, known to provide circuits of this type for use in dimming circuit applications, wherein the positioning of the finger upon the touch plate, and holding of the finger thereon, operates the dimming circuit from full off to full on, with finger removal at any intermediate point being adapted to maintain or select a particular operating level. A problem has arisen in connection with touch-type switching devices of the character described, in that the capability of producing and selling such devices commercially requires, as a practical matter, that the switching devices be listed by Underwriters Laboratories. This organization, however, requires compliance with certain established, rigid standards, for safety purposes, before it will list a switching device for a particular use and at a particular rating.
One of the requirements established by Underwriters Laboratories for switches of the character described, is a requirement for effecting a true separation of the electrical conductors that connect the switching circuit to a source of electrical power. This, in other words, means that a mechanical switch must be provided, in association with the touch-type on-off control function, whereby the switch can be completely disconnected from the source of electrical power. In the open condition of the switch, it is necessary to pass a high voltage withstand test established by Underwriters Laboratories, and as a result, a mechanical switch that will truly pass the test must be incorporated within the wiring device.
The problem that results as a practical matter, however, is that the supplementary electrical switch function has heretofore been achieved only through the provision of unsightly, exposed appendages to the wiring device, and this of course detracts markedly from the capability of the manufacturer to sell the switch product. A touch-type control switch, in the final analysis, is generally selected not only for reliability but also because of its aesthetic value, and it is thus readily seen that providing a mechanical switching device, fully exposed as it must be in order to permit its ready operation, has severely hampered the ability of the switch manufacturing industry, in developing a good commercial market for switches of this type.